Abstract Many studies have investigated the consequences of election outcome for one of the important public attitudes, political efficacy. The effect of election outcome on external efficacy has been confirmed by most previous studies, whereas the effect on internal efficacy is not clear-cut. By reconceptualizing internal efficacy based on the social cognitive theory of self-efficacy, this study argues that there are two conditions for an election outcome’s impact on internal efficacy: the expected difficulty of winning and the level of involvement in the election. By analyzing panel survey data collected for three Japanese Lower House elections, this study shows that election outcome exerted an impact on internal efficacy if the following two conditions were simultaneously satisfied: (1) winners/losers perceived that the election was difficult/easy to win, and (2) voters were deeply involved in the election process.